The present invention relates to an apparatus and a method for correcting a pattern film of lacking necessary portions of photomasks, reticles (hereinafter referred to as masks) used for manufacturing semiconductor devices or an integrated circuit through depositing film thereon with the use of ion beam.
FIG. 2 shows the principle of a conventional apparatus of correcting a pattern film. A gas gun 1 directs molecules of an organic compound 2 at a white defect 5 in a pattern 4 disposed on the surface of a substrate 3 for adsorption of the organic compound molecules. An ion beam scanning system 6 irradiates an ion beam 7 at a white defect 5 and scans the ion beam. As a result, a film of polymerised or carbonised organic compound molecules is deposited on the white defect. By repeating the scanning of the ion beam, a film is deposited to a thickness with required light-shielding when a sample is a photomak or reticle. The range of ion beam scanning depends on the size of a defect. In order to simplify the the structure of the ion beam scanning system 6, the current intensity of the ion beam is generally kept at constant, and the speed of ion beam scanning is adjusted at constant. The quantity of organic compound vapor from the gas gun is limited to the minimum so as not to pollute the inside of the vacuum chamber.
However, the drawback of the conventional apparatus for correcting a pattern film is that a film can not be deposited when the are of a defect is small.
FIG. 3 shows the relation between film deposition areas and frame numbers of ion beam scanning required to deposit a film of 2500.ANG. thickness. This is a typical example of correcting a defect of a pattern film when a film thickness is 2500.ANG.. Here, one frame means one complete scanning over the whole area of a defect. As shown in FIG. 3, as the film deposition area becomes 200 .mu.m.sup.2 or less, the number of frames required to obtain a predetermined film thickness increases. It further shows that film deposition becomes impossible when the area is 50 .mu.m.sup.2 or less. In the case of FIG. 3, the ion beam current is constantly maintained at 200 pA, and pyrene is used as an organic compound to be directed by the gas gun. Therefore, if the ion beam current is more than 200 pA, the number of frames for a required film thickness increases even when the film deposition area is more than 200 .mu.m.sup.2. And when the ion beam current is 200 pA or less, it becomes opposite. Therefore, when a film deposition area is small, the scanning time for a frame shortens because the speed of ion beam scanning is kept at constant. Consequently, during one frame scanning, the organic compound molecules to be polymerised or carbonised in the next frame can not sufficiently adsorb onto the current frame. Therefore, the drawback is that although an ion beam is irradiated, films can not be formed on top of another. Moreover, the surface of substrate and pattern is etched away due to spattering by the ion beam. This phenomenon becomes markedly stronger as the ion beam current becomes larger. This signifies that a film can not be obtained by the prior art when the ratio of film deposition area S to ion beam current I, S/I, is smaller than a certain level. In the foregoing, the phenomenon is described in case pyrene is used as an organic compound to be directed. However, the same phenomenon occurs in the case of other compounds.